Blast switch



p 3, 1963 I H. F. SWIFT 3,102,936

- BLAST SWITCH Filed Nov. 50, 1959 v INVENTOR HALLOCK F. SWIFT ATTORNEY United States The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to are discharge switches and more particularly to high current, low inductance switches that have a small insulating gap between the electrodes. 1

Heretofore arc discharges have been carried out between two electrodes to break down the medium between the electrodes. The spacing between the electrodes depends on the voltage to be discharged such that the spacing must be sufiicient to prevent pro-firing. Some arc discharge switches make use of an electrical discharge in the gap to initiate the discharge. These-switches can either have their electrodes enclosed in an envelope or open to the air. In order to prevent pre-firing of these switches, the electrodes are separated sufliciently that the air or gas between the electrodes provides suflicient insulation to prevent a discharge. In order to fire these switches an electrical discharge is provided in the gap to ionize the gas between the electrodes. Ionization of the gas between the electrodes permits a discharge across the switch. In these switches it is essential that the electrodes be separated by a certain distance.

The present invention is directed to an arc gap switch which makes it possible to place the electrodes close together and yet prevent a prediseharge. Such a switch can be used in smaller spaces than prior arc switches and yet carry as large or larger current loads than the prior arc switches.

It is therefore an object of the present invention to provide an insulating gap switch which can be placed in a small area and yet control high currents.

Another object is to provide an arc gap switch in which the switch is simple to construct, long lasting, and inexpensive.

Still another object is to provide a switch having a small gap between the electrodes for controlling high currents and high voltages.

Yet another object is to provide a high current, low inductance, low resistance are gap switch.

An additional object of the present invention is to reduce the insulating gap of a switch so that the inherent electrical resistance and inductance will be reduced.

The nature of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawings, in which:

FIG. 1 illustrates a cross sectional side view of a blast switch in a parallel plate arrangement;

FIG. 2. illustrates an enlarged view in perspective of a blast switch in a circuit;

FIG. 3 illustrates an enlarged view of a blast switch of a coaxial type;

FIG. 4 illustrates a sheet of insulation prepared with an aluminum foil therein adapted to be connected to a high current discharge; and

FIG. 5 illustrates a blast switch with the electrodes in end to end alignment with an insulation such as shown in FIG. 4 positioned between the electrodes.

The device of the presentinvention can be applied to parallel plate or coaxial conductors as well as other curtent "ice rent carrying geometry. The switch is formed by two electrodes separated by a small gap into which an insulating material is placed. The thickness and strength of the insulation being sufiicient to hold oil a discharge across the gap for the voltage applied. The insulation is ruptured by any suitable means such that the current will jump the gap between the electrodes for operation of the desired load element in the circuit. After operation, the insulation and rupturing mechanism can be replaced for another firing or operation of the load element. Such a switch is to be used in an electrical discharge circuit which carries high voltages. I

Now referring to the drawings wherein like reference characters refer to like parts throughout there is illustrated in FIGS. 1 and 2 a suitable blast switch 10 including parallel plate electrodes 11 and '12 which has an insulating sheet 13 of any suitable material therebetween. As shown, electrode 11 has a hole therein in which an electrical blasting cap 14 or any other suitable means is positioned for rupturing the insulating material in the general area of the hole. The blasting cap 14 is provided with suitable electrical connections 15 and 1-6 to which a suitable electrical source, not shown, is connected for setting oiT the blasting cap. FIG. 2 illustrates such a blasting switch in a circuit which has a condenser bank 21 as a source and a load 22 of any suitable nature,

- shown as a resistor. The circuit is suitably grounded at 23. Any suitable means, not shown for simplification of the drawings, can be used for charging the capacitor bank.

'FIG. 3 illustrates a modification of the blast switch used in a coaxial line including inner and outer conductors 24 and 25 separated by a suitable insulator 26-. As shown the inner conductor 24 is electrically broken and electrodes 27 and 28 are connected thereto. The electrodes are separated by a thin insulating material 13 of the thickness and strength sufiicient to prevent passage of the load voltage. Electrode 27 has an opening such as a hole therein into which a blasting cap 14 or any other suitable device is positioned to rupture the insulating material when desired.

In operation of the blast switch, the switch is placed in any suitable discharge circuit such as a capacitor bank charged to 20 kv. For such a high voltage in a parallel plate conductor circuit, parallel plate electrodes are separated by about 0.030 inch and a suitable insulating material such as a thin sheet of plastic is placed between the electrodes. A blasting cap 14 of about 2 grains is placed into the hole in one of the electrodes such that the blasting force end of the cap is adjacent to the insulating material. Dnce the switch and blasting cap is set up in the circuit, the condenser bank is charged to the desired voltage. The insulating material between the electrodes prevents a discharge across the electrodes and at the desired time the blasting cap 14 is fired. The blasting cap ruptures the insulating material between the electrodes in the vicinity of the blasting cap which permits a spark discharge across the electrodes and ultimately a complete discharge of the applied voltage across the switch. Any suitable load can be provided for the applied voltage. One application is for firing a projectile by electrically heating a suitable gas in a chamber which under sufiicient expansion and compression will force a projectile from the barrel of a gun.

FIG. 4 illustrates a modification of the insulation 13 between the electrodes which is provided with a thin sheet of aluminum foil 31 which has electrical lead lines 34 and 35 connected thereto. The aluminum foil is positioned within the insulating material such that the insulating material will still provide sufficient insulation in the above described switches. In operation, a high discharge through the aluminum vfoil explodes the foil causing the foil to rupture the insulating material to I I 3 permit a spark discharge across the gap and ultimate discharge of the voltage applied to the electrical circuit within which the switch is inserted.

For transmitting voltages of 20 kv. and currents of 2X10 amps, requires flat plate conductors as shown in FIGS. 1 and 2 or citherthick tubular conductors in a coaxial arrangement shown, in FIG. 3. FIG. 3 com.- prises an outer aluminum tube 25, a thin insulating sleeve 26, within the tube andan inner aluminum tube 24 Within the insulating sleeve. The switch is placed in the inner conductor tube as shown in FIG. 3. In each, the fiat plate and the coaxial conductors, the conductors are made to minimize inherent inductance so thatvery high energy delivery rates can be achieved.

In making use of the 'inswalting material with the aluminum foil therein as shown in FIG. .4; the aluminum foil is connected in the circuit as shown in FIG. 5 such that a capacitor discharge will explode the aluminum foil to disrupt the insulation and then the discharge from the main capacitor bank will discharge across the electrodes 32 and 33. It has been determined that flat thin aluminum fioil Will explode under high currents the same as a thin Wire in a circuit and on exploding the insulation Will be ruptured to the extent that .a discharge will be made between the electrodes. foil loaded insulating material can be used in switches such as shown in FIGS. 1, 2, and 3 without departing from the invention. In using an aluminum foil loaded insulator there is no requirement for making a hole in one of the electrodes for. inserting a blasting cap or other mechanism. i

The teaching of the present invention can also be carried out by use of a chemically explodable insulating material inserted between the electrodes. Such insulators will permit disruption of the insulating material over the entire area bet-ween the electrodes. Thus a large conducting area will be provided between the electrodes in a very short time thereby reducing the electrical resistance and inductance of the switch.

The teaching of the invention is not to be limited to The aluminum any specific electrode or insulating material or shape for it is obvious that the teaching can be carried out with many different switch designs and materials as well. as many diiferent types of insulating material.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claim the invention may be practical otherwise than as specifically described.

What is claimed is:

A high current, low inductance blast switch which comprises:

(a) first and second iClOSBlY spaced electrodes,

([2) a thin sheet of plastic insulating material completely separating said first electrode from said sec :ond electrode, v

(c) said insulating material having the thickness and insulating quality to prevent discharge of a high voltage between said first and second electrodes.

(d) an aperture in one of, said electrodes extending in a direction toward said insulation separating said electrodes,

(e) an electrically explodable blassting cap secu-red Within said aperture in said electrode, wherein (f) said blasting 'cap is positioned to disrupt said in sulation separating said electrodes to permit an electrical discharge across said spacing between said electrodes when said biasing cap is discharged. 1

References Cited in the file of this patent UNITED STATES PATENTS Lemp et al Nov. 16, 1886- 

